DESCRIPTION: Occupationally-related low back disorders (LBDs) are the leading cause of lost work days and the most costly occupational safety and health problem facing industry today. Epidemiologic surveys demonstrate that exercise and physical conditioning may act as a prophylaxis to reduce the incidence of occupational LBDs. How and why exercise and physical conditioning influence LBD risk remains unknown. To improve the intervention methods for control of occupational low-back pain, to improve rehabilitation of LBDs, and to identify individuals at increased risk of LBD, it is necessary to quantify how physical conditioning acts to limit low-back injury risk in occupational lifting tasks. Low-back injuries have been attributed to spinal load and spinal stability during lifting and manual materials handling tasks. Factors that contribute to spinal load and stability include lifting technique, spinal kinematic coordination, trunk muscle recruitment and co-contraction, and the design of the lifting task (weight, distance, etc.). It is proposed that exercise can modify lifting and spinal kinematics and muscle recruitment patterns, thereby influencing biomechanical risk associated with spinal load and stability. The goal of this research is to quantify how exercise and physical conditioning modify the biomechanics of lifting in manual materials handling and lifting tasks. Specifically, we intend to investigate factors that might contribute to improved spinal stability and reduced spinal load during simulated manual materials handling tasks. Subjects will participate in an eight-week exercise program in one of four protocols including either, aerobic exercise, strengthening, dynamic spine stabilization, or control (no exercise). Spinal load and spinal stability during simulated manual materials handling lifting tasks will be quantified before beginning the exercise program, midway through, immediately upon completion of the eight week exercise program and four weeks after termination of the exercise protocols. It is hypothesizes that the exercise programs will change the muscle recruitment patterns and spinal kinematics of lifting, thereby modifying spinal load and stability. Spinal load and stability will be quantified using published techniques, including efforts by the principle investigator, and based upon measurements of dynamic lifting kinetics, dynamic spinal kinematics I curvature and trunk muscle recruitment patterns (electromyography) recorded during the lifting tasks. This effort represents the first randomized-control study of exercise and physical conditioning on lifting biomechanics and associated risk factors for LBD.